refereed paper
irrigation advances
water SEPTEMBER 2012 93
Irrigation in the City of Stirling's
Parks and Reserves
The City of Stirling has 366 pumping
stations and associated infrastructure
that represent a $42M irrigation asset.
This system is designed to irrigate 740
hectares and to deliver a total output
of 5,226,750 kilolitres per annum. All
of the City's bores are licensed and
subject to quotas. The annual allocation
target of 7,500 kilolitres/ha/yr is an
average amount and is subject to review,
and may vary depending upon different
turf surface requirements.
The City's groundwater abstraction
records indicate that in 2006/2007
the annual allocation was exceeded
by approximately 22% depending on
seasonal factors. This resulted in part
from having to over-water several older
reserves to compensate for poor coverage
due to inefficiently designed irrigation
systems, and from having to compensate
for soil moisture deficit condition during
an extremely dry year with above average
temperatures. However, since the
implementation of the Water Smart
Parks strategy, the amount of water
licence allocation used fell to just 84%
of the total allocation in 2009/10 and
2011/12 (Table 1).
DoW, in conjunction with local
authorities, is currently developing the
requirements for Water Conservation
Plans. The Water Smart Parks strategy
is one avenue through which this is
being developed, and to ensure that the
overall allocation is not breached they
have advised that the new benchmark
allocation will be 7,500 kilolitres/ha/yr.
It is up to each local authority to ensure
that its usage is not in breach of the bore
license conditions issued to it, otherwise
permits could be revoked.
The City of Stirling implemented a 25-
year asset upgrading and replacement
program (based on industry standards)
for the irrigation assets. This is reviewed
annually prior to budget submissions and
adjusted depending on monitoring of the
system's performance. All new systems
are designed to Best Practice Standards
(i.e. to provide 85% coefficient of
uniformity in terms of sprinkler coverage
and wetting pattern). Several reserves
still operate with inefficiently designed
systems and are waiting to be upgraded
with successive budget programs. The
City's entire irrigation network is centrally
controlled and regulated through its
'Computerised Irrigation Monitoring
System' (CIMS). The system has the
capacity to monitor watering programs
in all irrigated reserves and to assess
systems performance in terms of flow
volume and
pressure at the
pump source.
Many of the
existing reserve-
based irrigation
systems have
been designed so
that a concept of
hydro-zoning can
be implemented
in conjunction
with the process
of eco-zoning. In
addition, the City is
nearing completion
of a project, funded
under the National Community Water
Grant program, for the refinement of a
soil moisture monitoring system that could
be directly linked into the CIMS unit.
Planning for Different Scenarios
In the development of the Water Smart
Parks strategy the following three
scenarios were evaluated in terms of
savings on water usage and annual
operating costs (Figure 2).
• Scenario 1 represents a reserve
previously operating on an inefficiently
designed irrigation system, but
upgraded to provide an 85% coefficient
of uniformity. It was estimated that
with a simple upgrade a reduction in
annual water usage by up to 13%, and
a corresponding reduction in the annual
operating cost, could be realised.
• Scenario 2 follows on from the Scenario
1 reserve, but with the introduction of
hydro-zones around peripheral areas.
These are areas infrequently used for
recreation and where turf quality can be
sustained with a lower watering regime
(Short, 2002). It is estimated that this
treatment could achieve a reduction
in annual water usage of 19%, while
a corresponding reduction in annual
operating costs could be realised in
comparison to the original unimproved
irrigated reserve.
• Scenario 3 follows on from the Scenario
1 reserve, but in this instance with the
introduction of hydro-zones and eco-
zones. Eco-zones are portions within
hydro-zones converted to native tree
and shrub plantings. Such areas are
eradicated of the original turf and are
heavily mulched, thereby removing the
necessity for irrigation. It was estimated
that with this treatment a reduction
of 42% in annual water usage and
a reduction in annual operating costs
could be realised in comparison to the
original unimproved irrigated reserve.
Implementation of these scenarios
is also expected to deliver other
beneficial outcomes, such as lower
maintenance of the asset base,
significant energy savings, and
enhanced recreational amenity values.
The Process of Prioritisation
This initiative categorises parks into
'zones', ie, 'eco-zones' or 'hydro-
zones'. These zones may have different
watering needs dependent upon zone
use, resulting in overall reduced watering
requirements. An example showing how
this works is presented in Figure 3.
Zone Categories:
Table 1. Groundwater use in relation to water licence allocation from 2006/07 until
2011/12.
Financial Year Water Licence
Allocation
Amount of Water
Licence Allocation Used
(KL)
Amount of Water
Licence Allocation Used
(%)
2006/07
5,226,750
6,376,635
122.00%
2007/08
5,226,750
6,272,100
120.00%
2008/09
5,226,750
5,435,820
104.00%
2009/10
5,226,750
4,385,243
83.90%
2010/11
5,226,750
5,174,483
99.00%
2011/12
5,226,750
4,390,470
84.00%
Figure 2. Cost effectiveness of upgrade scenarios.
Cost effectiveness of three upgrade scenarios
Water savings
Maintenance cost savings
300
250
200
150
100
50
00
5
10
15
20
25
30
35
40
45
50
Savings (% of base case)
Capital costs ($000)
3 Plus Ecozones
2 Plus Hydrozones
1 Improved CU
Evaluation of scenarios: 1 Upgrade of irrigation system for improved sheduling and Coefficient of Uniformity (CU).
2 Redisign of irrigation system to introduce additional Hydrozones (passive turf areas).
3 Redesign of irrigation system, introduction of Hydrozones and Ecozones (rainfed gardens)
Most cost-effective